Conventionally, multiple servers or the like are installed in data centers, corporate server rooms and the like. The temperature in such server rooms or the like rises due to the heat generated by the multiple servers. This increased temperature may give rise to server runaway or malfunction. Accordingly, air conditioning systems are used, in the server rooms, to maintain a constant temperature of the room as a whole. Such air conditioning systems operate substantially full-time, also in winter.
For conventional air conditioning systems for such server rooms or the like, low-temperature air (cold air) blown from an air conditioning device is supplied into the server room while contacting with the servers in server racks to cool the servers and stabilize the room temperature in the server room. As a result, a circulation scheme is resorted to wherein air (warm air) that is warmed by the heat of the servers is returned from the server room to the air conditioning device, and is cooled by the air conditioning device, to be cold air again that is then blown out into the server room, to supply cold air once more.
Known conventional technologies include for instance those described in Patent documents 1, 2, 3, 4, 5.
Patent document 1 is an invention, relating to indirect outdoor air cooling, that involves a configuration wherein a refrigerant pump is operated, instead of a compressor, when, for instance, outdoor air temperature is low; as a result, a cooling operation (cooling of a refrigerant using outdoor air) can be carried out simply by causing a refrigerant to circulate by the refrigerant pump. In the invention of Patent document 1, controlling of increasing and reducing the air volume of an exterior side fan is proportional to the difference between an interior temperature and a set value.
Patent document 2 relates to an air conditioner including the refrigeration cycle, which has, for instance, a compressor and a water-cooled condenser, and a cooling water circulation cycle that has for instance a cooling tower and a cooling water circulating pump to circulate the cooling water in the water-cooled condenser. In the invention of Patent document 2, for instance, the cooling amount of the cooling tower is increased, the water supply amount of the cooling water circulating pump is increased, the rotational speed of the compressor is increased, the air volume of the interior fan is increased, and the degree of opening of an expansion valve is controlled, when the interior temperature is equal to or higher than a predefined value.
The control scheme in Patent document 2 includes first control to fourth control, as control modes. In the first control, the devices in the refrigeration cycle are operated at a low load, and the devices in the cooling water circulation cycle are operated at a high load. In the second control, the devices in the refrigeration cycle are operated at a high load, and the devices in the cooling water circulation cycle are operated at a low load. In the third control, the devices in the refrigeration cycle are operated at a high load, and some of the devices in the cooling water circulation cycle are operated at a low load and the rest at a high load. In the fourth control, the devices in the refrigeration cycle are operated at a low load, and some of the devices in the cooling water circulation cycle are operated at a low load and the rest at a high load.
Patent document 3 is an invention, relating to indirect outdoor air cooling, which involves a configuration wherein a refrigerant pump is operated instead of a compressor, depending on the situation, as in Patent document 1 above. The control scheme in Patent document 3 involves switching from a compression cycle to a refrigerant pump cycle if, for instance, an outdoor air temperature is equal to or lower than a set value, or if cooling capacity is equal to or smaller than a set value (for instance, desired value of interior temperature), or if a compressor frequency is equal to or lower than a set value.
Patent document 4 is an invention relating to indirect outdoor air cooling, which involves a configuration, wherein depending on the situation, a refrigerant pump is operated instead of a compressor, as in Patent documents 1 and 3 above. The control scheme in Patent document 4 involves switching from a refrigerant pump cycle to a compression cycle if, for instance, the outdoor air temperature becomes equal to or higher than a set value, or if the interior temperature becomes equal to or higher than a set value, or if the refrigerant flow rate is abnormal.
Patent document 5 is an invention relating to indirect outdoor air cooling, which involves a configuration, wherein depending on the situation, a refrigerant pump is operated instead of a compressor, as in Patent documents 1, 3, and 4 above. The control scheme of Patent document 5 involves changing over from an indirect outdoor air cooling cycle to a vapor compression type cooling cycle when the number of times that a result of measuring a refrigerant flow rate exhibits a value not greater than a preset fixed value exceeds a predefined number of times within a predefined lapse of time.
Patent document 1: Japanese Patent No. 3354882
Patent document 2: Japanese Patent No. 4074422
Patent document 3: Japanese Patent No. 3967033
Patent document 4: Japanese Patent No. 3995825
Patent document 5: Japanese Patent No. 4145632
In the conventional technologies of Patent documents 1 to 5, the indirect outdoor air cooling capacity fails still to be maximally utilized. One cause of this is that, for instance, the schemes that are resorted to involve switching to either cycle from among two cycles, namely a compression cycle and a refrigerant pump cycle.